My current player on Official has a reported blood type of O-
However, when I collect their blood with a blood collection kit the bag gets labeled as being O+. I've not tested this for other survivors and blood types as I'd previously not seen bags getting a label (recent feature I gather)?
I'm hoping this is just a reporting bug and not that the bag of blood somehow became O+ in the database. If it has you'll have some very upset survivors on your hand unless this is corrected as well.
That being said, IF the bags have been converted to O+ I highly suggest that the developers remedy this by making all CURRENT O+ blood into O-. That may see heavy handed, but so is the reverse considering the bug. At least O- is the universal blood so fixing this bug and correcting any data issues will have the least impact to those impacted. For example, until I took notice of this, given his O- blood type, I'd filled a number of bags with this survivor the last 2 weeks. I'll go to the stashes I've stored those in to see what they report but I suspect they'll all be wrong given I've tried it 3 times now since first noticing.
See screenshots in additional information.