I don't think the government would think of it like 'retroactive'. For example with Pirate, (not DPR but the ponzi scheme pirate) he argued in court that the SEC didn't have standing as Bitcoin wasn't real money, (and it wasn't at the time) but a judge says, "Looks like money, smells like money, buys like money- it's money" and just like that Bitcoin came under SEC regulations.
I don't think that is correct. I would agree with 'just like that,
Bitcoin-denominated securities came under SEC regulations'. Just as do FRN-denominated securities, while FRNs themselves do not.