I'm terrible in a sumo stance. I've always been told that whatever you can deadlift in a close stance, you'll be able to deadlift more sumo. Just by default. To the extent that you can never train sumo, then do sumo deadlifts and they'll be bigger and heavier and stronger. Contrary to such claims, I think the most I've sumo deadlifted is 100kg, and that number ain't climbing without some dedicated effort (which I feel no compulsion to do -- my thighs already rub together all the time, I don't want more muscle on my adductors).
Between seizures, illness, injuries, work and home life, I think we've all done our fair share of "irregular training" this year.