I was told yesterday by the representative of a large dji distributor about the TB50 batteries:
"There is a bad batch that was released in quarter 3 of this year and we are trying to get through those.
If you received some in July of this year then they should be from Q2 and not including in the bad batch.”
As to the TB55 batteries, I don't know the answer for those as I only ordered TB50's in Nov. '17 (for a M200) and batteries in early July of '18.