Reporting back, as promised.
Thank you Taz2 for the link. I had recently remembered that I *was* vaguely aware of this and (it turns out!) had even asked a question on MM a few years after my hysterectomy because I was concerned. I blame meno brain for the fact that I had since forgotten.
Anyway - have just had a conversation with my GP... She asked me what were my plans HRT-wise, and I thought 'blimey - she's forward-thinking - she's going to ask me if, at the age of 65, I want to go on to systemic HRT' - but no, as it turned out. She thought that I was 'already' on systemic HRT, having (I gathered) become confused by the fact that I use two types of oestrogen - Vagifem and Ovestin, despite the fact that both are topical. I did try systemic for a while many years ago (hence my concern referred to above) to try to get VA under control, but was having such bad side effects, and no good effects on the VA, that I stopped within a year.
I wouldn't expect the GP to remember me out of all the thousands of other patients but, given the fact that she'd apparently gone to the trouble of emailing two consultants to ask for advice before contacting me out of the blue, I'm surprised she hadn't looked more closely at my records. The last prescription for Oestrogen gel I had must have been around 7 years ago and she actually prescribed the Ovestin last year after an email exchange we'd had about me wanting to try it on the vulval area. My gob was well and truly smacked, honestly.
The upshot is - as I'm not on systemic HRT, there's no need for me to do anything - all cancelled. Had I not queried it though, I could already have been taking the medication. I'm so glad I asked.
(If anyone is interested in current thinking on the whole progesterone challenge thing, it seems that of the two consultants she asked, one said it wasn't necessary and the other said it was probably worth doing, so still no concensus, it seems).