Thanks for the responses, everybody (especially Henning). I've sent an inquiry to Fujifilm USA at
https://www.fujifilm.com/us/en/business/professional-photography/film/contact and will relay their response back here should I receive any reply. (I'm doubtful that I will get any response from this company, though, at least their photography division, as I hear they are famously uncommunicative with their customers.)
Meanwhile B&H is one of the few US retailers with any Velvia 50 in the 120 format still in stock. I just today received a 5-roll pack from B&H, ordered last week and shipped on Monday. It expires April 2021 (yes this month) and is the same lot number (5232012) as half of all the 120 Velvia 50 that I bought and accumulated from various US retailers between Spring and Fall of 2020. FYI, the other half of what I accumulated over that time, also from US retailers, is expiration-dated September 2021, lot number 5242012. That's it. Go figure. I deduce from this that even major US retailers (and I believe B&H is the biggest in North America) have not received a fresh shipment of this film from Fuji in 6-12 months. In comparison, during "normal times" over the last decade, this film has always come to me with expiration still 6-12 months or more into the future.
Given those timings, it makes me suspect that Fuji has not been able to (or has chosen not to) manufacture much, or any, of this film since shortly after the pandemic got underway, whether due to shortages of raw materials, problems with distribution, issues with coronavirus safety in the factory, or whatever. I wonder what's up and when it will get back to normal.