Off the top off my head:
2015
-No Falkirk- the electoral college remains, and Corbyn loses to Burnham despite having the overwhelming backing of the membership and the unions
-Corbyn doesn't run in the first place/fails to get on the ballot
-Corbyn doesn't get on the ballot because Ummuna stays in the contest
-Corbyn doesn't run because one of the other MPs touted as a standard bearer of the left puts themselves forward instead. Trickett, Lavery, McDonnell, or even one of the new intake such as Clive Lewis were all suggested. I could even see Chris Williamson going for it had he got the few dozen more votes he needed to survive in Derby North in 2015. Not all of those candidates could win, but I feel like Lewis or Trickett would be in with a decent shout, and either of them would have very interesting implications for the party's approach to Brexit.
-Labour votes against the Welfare Bill, or Burnham resigns to vote against it-probably wouldn't change the final outcome, but would result in a more narrow margin of victory for Corbyn, placing him in an even weaker position in his first year in charge
2016
Britain votes Remain- not necessarily a Corbyn related PoD, but it would be very interesting to see how long a leadership challenge (which was probably inevitable at some point) was delayed, and whether his opponent would stand a better chance if the contest was a year or so later than IOTL. Also, a UKIP surge gives Labour a stronger chance of winning the next election (possibly even with a majority) if it can be sustained till then. Conversely, no Brexit divide might also means more defections to ChUK.
Corbyn resigns during the coup as he was allegedly close to doing, or Watson succeeds in getting the NEC to keep him off the ballot. Unless there was a quid pro quo that allowed Lewis or some other hard left candidate on the ballot, the next leader would probably be Owen Smith or some other soft left candidate- and the hard left would be massively alienated from Labour.
-The PLP chooses a different challenger to Corbyn. Angela Eagle is the most obvious one, but I think she would if anything do slightly worse than Smith. Nandy would give him more of a run for his money due to the fact it would be far harder to cast aspersions on her left wing credentials. Even if she didn't win, a smaller margin of victory for Corbyn would be perceived as weakening his mandate, possibly paving the way for a second leadership challenge at some point in the future.
-Starmer isn't appointed Shadow Brexit Secretary-potentially leading to a smoother path to victory for RLB or whoever Corbyn's preferred successor turns out to be.
2017
Labour loses Stoke on Trent Central to UKIP- probably because they go for a strong local candidate over Nuttall. Probably leads to a mini-UKIP resurgence, and leads to fresh calls for Corbyn to go-though I doubt he would do so immediately.
Lewis does not resign from the Shadow Cabinet over A50-possibly stymieing the promotion of RLB, and putting him in a stronger position to be seen as the natural successor to Corbyn.
No 2017 GE. Much like no Brexit, the main question is whether disaffection with Corbyn would set in before the end of the parliament leading to him being ousted, or whether he might limp on till the next GE.
A longer 2017 Campaign/an earlier Grenfell Tower Fire-the momentum Labour accumulated from this could be enough to enable them to form a minority government- and possibly become the largest party
A shorter campaign/no dementia tax. The Tories win a majority, but not the humongous one they were looking at at the outset of the campaign. A sweet spot would be one large enough to pass the WAB at third time of asking off the back of Labour rebels-which could cause massive internal division, and is probably your best chance of their dire polling at the fag end of the May era actually enduring until a GE. Corbyn resigns if Labour lose more than fifteen seats. If the result is better than that, he might try and stay on, but face far stiffer resistance from the mainstream PLP.
2018
-Labour adopts IHRA definition in full immediately
2019
Watson is ousted by the NEC at the 2019 Conference- this would likely create an absolute shit storm within the PLP that could potentially mean more defections right on the brink of a GE.
The Conference votes to campaign for Remain in a second referendum-probably enables Labour to maintain a stronger hold on Remain voters at the GE, perhaps doing slightly better in terms of seats.