Possibly a non-issue due to the introduction of comprehensive tab-completion, but I'm reporting just to be safe. Also possibly a duplicate of MC-121634.
Help texts provided to the user after issuing an invalid/incomplete command (in 1.12.2) aren't always just the syntax help (see also MC-121634), but sometimes there would be some amount of additional information given. For example, /scoreboard teams option testTeam seeFriendlyInvisibles would print more than a simple usage string one would get from /help:
Usage: Valid values for option seefriendlyinvisibles are: true and false
Confirmed.