"We are well aware that the labeling of the seasons on these DVDs are confusing, but for some reason FOX in the UK has decided to categorizes the episodes differently to FOX in the States."
"Originally "Family Guy" was only available on DVD in the UK and were sold as seasons 1, 2 and 3. Then the States caught up by selling those seasons as two volumes. Since then FOX has opted for global releases, which seems to have resulted in the UK DVDs (as well other non-region-1 areas) continuing to be labelled as seasons despite not being complete seasons."
There's really is no reason for confusion when it comes to the dvd sets.
After Season 3, the sets have been released as identical "Volumes" for all regions but remain labeled as "Seasons" (or "Series") outside R1, despite NOT being complete seasons. In fact with the exception of Season 3, there has never been a complete single season set for any region.
All information below is based on how Family Guy aired originally & presently on FOX in the U.S.
Region 1 ......................................................Region 2,3,4
"Volume 1" (Complete Seasons 1 & 2) = "Season 1" (Complete Season 1 & Seven episodes of Season 2)
"Volume 2" (Complete Season 3) = "Season 2" (Remaining 14 episodes of Season 2)
N/A = "Season 3" (Complete Season 3)
(Sets now become identical but named differently)
"Volume 3" (First 13 episodes of Season 4) = "Season 4" (First 13 episodes of Season 4)
"Volume 4" (Remaining 14 episodes of Season 4 (minus "Stewie B. Goode", "Bango Was His Name-O" & "Stu & Stewie's Excellent Adventure")) = "Season 5" (Remaining 14 episodes of Season 4 (minus "Stewie B. Goode", "Bango Was His Name-O" & "Stu & Stewie's Excellent Adventure"))
"Volume 5" (First 13 episodes of Season 5) = "Season 6" (First 13 episodes of Season 5)
"Volume 6" (Remaining 5 episodes of Season 5 and the first 7 episodes of Season 6 (minus "Blue Harvest")) = "Season 7" (Remaining 5 episodes of Season 5 and the first 7 episodes of Season 6 (minus "Blue Harvest"))
"Volume 7" ("Back to the Woods", "Play it Again Brian", "The Former Life of Brian" & "Long John Peter" and Season 7's episodes - "Love Blactually" to "The Juice Is Loose!") = "Season 8" ("Back to the Woods", "Play it Again Brian", "The Former Life of Brian" & "Long John Peter" and Season 7's episodes - "Love Blactually" to "The Juice Is Loose!")
"Volume 8" (Season 7's episodes: "FOX-y Lady", "Not All Dogs Go to Heaven", "420", "Stew-Roids", "We Love You Conrad", "Three Kings", "Peter's Progress" & Season 8's episodes: "Road to the Multiverse", "Family Goy", "Spies Reminiscent of Us", "Brian's Got a Brand New Bag", "Hannah Banana", "Quagmire's Baby", "Jerome is the New Black" & "Dog Gone"), it does not contain the 'banned' episode "Partial Terms of Endearment" = "Season 9" (Season 7's episodes: "FOX-y Lady", "Not All Dogs Go to Heaven", "420", "Stew-Roids", "We Love You Conrad", "Three Kings", "Peter's Progress" & Season 8's episodes: "Road to the Multiverse", "Family Goy", "Spies Reminiscent of Us", "Brian's Got a Brand New Bag", "Hannah Banana", "Quagmire's Baby", "Jerome is the New Black" & "Dog Gone"), it does not contain the 'banned' episode "Partial Terms of Endearment"
"Volume 9" (the rest of Season 8: "Business Guy", "Big Man on Hippocampus", "Dial Meg for Murder", "Extra Large Medium", "Go Stewie Go", "Peter-assment", "Brian Griffin's House of Payne", "April in Quahog", "Brian & Stewie", "Quagmire's Dad" & "The Splendid Source") minus "Something Something Something Dark Side" & the first 3 episodes of Season 9: "And Then There Were Fewer", "Excellence in Broadcasting" & "Welcome Back Carter") = "Season 10" (the rest of Season 8: "Business Guy", "Big Man on Hippocampus", "Dial Meg for Murder", "Extra Large Medium", "Go Stewie Go", "Peter-assment", "Brian Griffin's House of Payne", "April in Quahog", "Brian & Stewie", "Quagmire's Dad", "Partial Terms of Endearment" & "The Splendid Source") minus "Something Something Something Dark Side"
(& the first 3 episodes of Season 9: "And Then There Were Fewer", "Excellence in Broadcasting" & "Welcome Back Carter")
The U.S. banned episode, "Partial Terms of Endearment" is included in the U.K.'s "Season 10" but since it was released as a stand alone DVD in R1, it is not included in "Volume 9"
"Volume 10" (The rest of Season 9: "Halloween on Spooner Street", "Baby, You Knock Me Out", "Brian Writes a Bestseller", "Road to the North Pole", "New Kidney in Town", "And I'm Joyce Kinney", "Friends of Peter G", "German Guy", "The Hand That Rocks the Wheelchair", "Trading Places", "Tiegs for Two", "Brothers & Sisters", "The Big Bang Theory" & "Foreign Affairs" ) Minus "It's A Trap" = "Season 11" (The rest of Season 9: "Halloween on Spooner Street", "Baby, You Knock Me Out", "Brian Writes a Bestseller", "Road to the North Pole", "New Kidney in Town", "And I'm Joyce Kinney", "Friends of Peter G", "German Guy", "The Hand That Rocks the Wheelchair", "Trading Places", "Tiegs for Two", "Brothers & Sisters", "The Big Bang Theory" & "Foreign Affairs") Minus "It's A Trap"
"Volume 11" = "Season 12" | Release Dates Unknown
Both sets will presumably contain all or most of the episodes that aired as Season 10 | Lottery Fever | Seahorse Seashell Party | Screams Of Silence: The Story of Brenda Q | Stewie Goes for a Drive | Back to the Pilot | Thanksgiving | Amish Guy | Cool Hand Peter | Grumpy Old Man | Meg & Quagmire | The Blind Side | Livin On A Prayer | Tom Tucker: The Man and His Dream | Be Careful What You Fish For | Burning Down the Bayit | Killer Queen | Forget-Me-Not | You Cant Do That On Television, Peter | Mr. and Mrs. Stewie | Leggo My Meg-O | Tea Peter | Family Guy Viewer Mail #2 | Internal Affairs
Although it should be noted that the releases tend to only contain 13 to 15 episodes, it's unlikely all 23 episodes will be included in the next set, but of course, time will tell.