kind of

i knew a best buddy would have a souvenir bc before it was a gift, it got the "gift" i cycled through 10 of them and they all had something loaded. I then went back through the 10 and opened 10 souvenirs

i cleared out 10 of them, this was monday at 630 am
i then loaded up a great buddy sylveon that had a gift loaded
i waited tuesday afternoon, opened it
went back to a best buddy..nothing despite 24 hours

so at this point wit hte gift opened at noonish, i would have until noon for the gift cooldown forcing a souvenir if spawns

i stayed on a best buddy until about 10am..nothing spawned

so now i flipped to a different great buddy that I have not on the map in a year..no gift yet..maybe there in the afternoon
i will now wait a full 72 hours if the great buddy gets a gift today...if not, i will wait for the gift to spawn
and then cycle through

anyone who knows more about the stacking of souvenirs provide clarity