Not sure if this is intended or not, but "correct" Player UUIDs aren't present in their Datatag. What I mean by "correct" UUID is that the UUID that appears in UUID look up sights and OwnerUUID tags of pets match none of the datatag in a player. Taming wolves etc alters their OwnerUUID to match the players UUID found on look up sites but there's no clear way this is achieved.
If this is intended, adding the "correct" UUID would be very useful for mapmakers to spawn pet that are automatically tamed via
/execute store . . . data get . . .
The information in there is correct, just in a different format. As per the wiki:
The key issue is that those numbers are displayed in decimal, while UUIDs are normally displayed in hexadecimal. Converting the two numbers into hex (the windows calculator can do this, in programmer mode), shows exactly what you might expect:
UUIDMost: 6995920856050712741 is 611680F3DDA640A5 in hex
UUIDLeast: -6879446167797835757 is A0874C28C4FCD813 in hex
Join those together, and you get 611680F3DDA640A5A0874C28C4FCD813 – which should look familiar.
Granted, it being difficult to convert between the two different formats is still annoying, but changing the format of that data is a feature request, not a bug (consider posting it in the new /r/TechnicalMCS or just the regular /r/minecraftsuggestions).