After rewatching the show, I got curious and sonewhat confused and decided to configure the timeline with all those retcons and stuff and try to accurately breakdown the "Degrassi Timeline". Most people probably already know the information about the timeline but I thought it would be fun to decipher the Degrassi Timeline on my own. There might be a flub somewhere in the information but this is what I have managed to form with the info we've got.

Degrassi Junior High begins in 1987 and the first two seasons are supposed to represent the 1987 - 88 school year, with Emma being born at the end of 1988 school year. Season 3 is then supposed to represent the 1988-89 school year. After DJH finished, Degrassi High is released and the first season of Degrassi High takes place during the 1989-1990 school year and Season 2 is during the 1990-1991 year. Finally School's Out is supposed to be the summer of 1992. Everything makes sense at this point but now here's when the first retcon came into place. With Degrassi TNG trying to be caught up in modern day timing at that point, Season 1 is set in the 2001-2002 school year meaning all the events in DJH and DH were all phased one year forward into the future meaning the first two seasons of DJH now represents the 1988-1989 school year and S3 is the 1989-1990 school year. The only two season of DH represent 1990-1992 school years and School's Out is set in the Summer of 1993 now. Then continuing the DTNG timeline, S2 to S5 of DTNG is supposed to be a new year each season (2002- 2006) then Season 6-7 (2006-2007) and 8-9 (2007-2008) are supposed to be a semester a season meaning by the end of Season 9 it is 2008. The timeline remains consistent up until this point. Then here's where the Degrassi Timeline starts to get a bit messed up. For Season 10 the writers tried to match the show into real time so they phased the show two years forward into the future technically while trying to make it seem like the last two seasons took place during the last school year, meaning all the events in Degrassi prior to this season have been pushed two years forward for consistency. (Catch Up: With the Season 10 retcon, DJH now represents the 1990-1992 school years, DH is the 1992-1994 school year, School's Out is the Summer of 1995, DTNG Season 1-5 is the 2003-2008 years and Season 6-7 are 2008- 2009, Season 8-9 are the 2009-2010 school year at this point with all the retcons). Season 10 to 11A is supposed to be the 2010-2011 school year and timeline seems to be consistent for a shortwhile. Now here comes the final retcon (that I am at least aware of lol). Season 11B to 12 is supposed to be 2011-2012 school year but they wanted to catch up with real time again (making the graduating class of Season 12 become the class of 2013 instead of being the class of 2012 originally) meaning every season prior to Season 13 has been pushed a year forward into future (Catch Up #2: Due to the retcon, DJH now represents the 1991-1993 school years, DH is the 1993-1995 school years with School's Out being set in the Summer of 1996 now. DTNG Season 1-5 is now set from 2004 up until 2009, Season 6-7 is now in the 2009 to 2010, school year, Season 8-9 is the 2010-2011 year, Season 10 to 11A is the 2011-2012 year, Season 11B to 12 is supposed to represent the 2012 to 2013 school year and finally Season 13-14 is the 2013 to 2014 school year)

Retcons:

Class 06 is now the Class of 09

Class of 07 is the Class of 2010

Class of 08 is the Class of 2011

Holly J's Class is technically the Class of 2012

Eli's Class is the Class of 2013

Clare's Class is now the Class of 2014 (technically before the Season 10 retcon they were supposed to be the Class of 2011; after the Season 10 retcon they were going to be the Class of 2013 then the Season 12 Graduation retcon sets them forward to be the Class of 2014)

Overall breakdown with all retcons:

DJH Season 1-2: 1991-1992

Season 3: 1992-1993

Degrassi High S1: 1993-1994

Season 2: 1994-1995

School's Out: Summer of 1996

(Snake's Class is the Class of 96 and Joey's Class is the Class of 97)

DTNG Season 1-5: 2004-2009

Season 6-7: 2009-2010

Season 8-9: 2010-2011

Season 10-11A: 2011-2012

Season 11B-12: 2012-2013

Season 13-14: 2013-2014

(and just for consistency)

DG:NC Season 1-2: 2014-2015

DG: NC Season 3-4: 2015-2016

Hopefully this was broken down properly and made things a little easier in terms of understanding the the fluctuating timeline of Degrassi.