Weirdly enough, the ill-fitting stardates were added to the episodes in the final rewrite. TrekCore has a selection of penultimate scripts for the episodes, including an <insert nifty plot resolution here> version of "Angel One", and those lack the contradictory bits, either omitting stardates or having more suitable ones.
Apart from that, Yar largely plays bit parts in her "posthumous" episodes, and could easily have been left out of those stories - ¨save for "The Arsenal of Freedom", where not having her front and center when key officers were trapped or incapacitated would have been odd.
It's also odd that the stardates of "Lonely Among Us" follow so soon after "Datalore", which supposedly is a fairly long adventure where Lore first is assembled, then mingles with the crew for some time. But by no means impossible. I just feel the heroes should be more wary of the possibility that somebody who looks like a known entity actually has Evil Inside in the immediate aftermath of the Lore adventure!
Timo Saloniemi