I suspect you are bang on there Steve, and if it is, then you'll need to get it looked at to confirm. According to conventional wisdom, P. josephinae flies later than flavifrontella, but conventional wisdom isn't always right! (and it's a poor way to confirm an id too, resulting in circular logic: if all early flying Pseuds are recorded as flavifrontella, then the evidence from the record books will be that all early flying Pseuds are flavifrontella!) I'll bet yours will be flavifrontella though
As to rarity...who else is looking for them?