Hi sadielouise78
If your last natural period was less than 12 months ago then you are deemed peri-menopausal still ( 12 months need to have elapsed without a period before you can say you are post-menopausal). That being the case cyclical HRT is prescribed and yes it does give a withdrawal bleed. If you don't fancy that and you really are very late peri-menopause and eg in early/mid 50's then you could ask your doc to try continuous combined (no bleed HRT) - but you might get breakthrough bleeding?
However many of us on here would recommend ALWAYS starting with a cyclical HRT even if post-menopause because it enables you to see if that dose of oestrogen works for you, and more to the point if you are OK with the particular progestogen in that HRT preparation - as there are several different types and not all women get on with them.
I still have a withdrawl bleed and I'm in my mid 60's as there is no way I want to take progesterone all the time. However I am on a long cycle ( with approval of my GP) so only take it every 6-8 weeks.
You're right you will never know the exact date of your menopause but does it matter? I don't know mine. I started HRT at just under 54 having had my last natural period at 53.5. I might never have had another one or I might have had a few more and I will never know

Also sometimes during peri-menopause the womb lining builds up as the ovaries begin to fail and follicles start to ripen (producing oestrogen) but don't actually "pop" - so the lining can get thicker and thicker. The next time you ovulate the period would then be very heavy as there is a lot to shed. If you start taking HRT the same thing can happen - the first bleeds on sequential HRT may be quite heavy ( which is good as the lining is being shed) and even on continuous combined HRT many women experience spotting or bleeding in the first few months as the lining sheds sporadically and then eventually thins and stays thin (due to the continuous progestogen).
If you want to take HRT and you are peri-menopausal but don't want to bleed then the Mirena coil is a good option for the progestogen part and then you can add oestrogen at the dose you want.
Hurdity x