As to volunteers, many seeds simply wait until the soil temperature is optimal before they sprout. Tomato seeds do have a surrounding gel that inhibits germination. That gel may need some time to degrade naturally in soil. It is well known that tomato juice inhibits germination, which is one reason why tomatoes that fall to the ground don't germinate their seeds readily. Indoors? If you keep the temps at 70-80F, well-prepped seeds should germinate promptly.

Temps inside always 70 or more and this happens every year for at least 5 years. Weird.

I've has a few oddball late geminations like that in the past. I'd start 3 tomato seeds in one cell and 2 of them pop up. A month later the 3th one pops up sometimes after I even transplant that cell into a larget pot. It may be Mother Nature's genetic way of survival if a late freeze kills off the early birds? ....Last year I planted Black Seeded Simson lettuce seeds in it's own plot, none went to seed (composted beforehand) but 2 BSS plants popped up this Spring in that same plot.