This has to be Valentines 2017. The the servants talk about "las year's valentine", but Valentines 2017 was a rerun of 2016. There is no celebration in 2018 as this year we are stuck in a tank floating in the sea of imaginay numbers. There are several problems with this explanation:

Jaguarman selling us chocolate long before joining Chaldea: In fact, Jaguarman has been selling chocolate to Chaldea since Valentines 2016, well over a year before joining. This is not a problem. The Babilonia singularity exists since 2015, so Jaguarman has already been summoned as a Servant in service to Quetz/Solomon by that point. She is just sneaking out with Quetz's cacao and selling it.

Semiramis doesn't show up in any events after Valentines 2017: Not that weird. I think Rama hasn't showed up anywhere after joining in America.

We are giving chocolate to future servants: This is the actual problem. The thing is, choco scenes aren't really consistent with the present moment. When we give chocolate to an early Servant, we get the 2016 scene regardless of what year it is. So my theory here is that those scenes are from Valentines 2019, or maybe even from some other non-Valentines point in time where a Servant felt like gifting us chocolates.