Although some may buy images in advance for their projects, I don't see that trend of "sales months in advance, nothing next to the event".
I often have seasonal sales right next to the date, I even sold New Year images right after New Year and a shamrock illustration the day after St Patrick's.
I haven't sold perhaps any of my Valentine-related images lately, except for a heart illustration that has an odd high performance in BigStock and makes 90% of the latest sales I had there, but I sold some St Patrick and Easter ones this week (so 1-2 months in advance only).
Having said that, overall this month is slower than I had expected, with DT falling deep in my best earners list.
Regards,
Adelaide