Re the lining.
If you are post-menopausal and taking cyclical HRT, the womb lining builds up from the oestrogen and then the progestogen part of the HRT changes this built-up lining structurally. When you then stop the progestogen - the lining breaks away as an artificial period - sometimes called a withdrawal bleed as it's not a true period. If the dosages are right then all the lining comes away and it never gets over thick. Sometimes women don't bleed on this regime and this means usually that the progestogen dose is plenty high enough for the lowish oestrgoen dose.
If you take continuous combined HRT which is both hormones together all the time, then after the initial settling in period of time when you might get some bleeding and spotting, eventually the progestogen intereferes with the ability of the womb lining to grow so it stays thin. Again if the balance is wrong it does continue to grow and then break away sporadically - after 6 months of a regime like this if bleeding continues then it should be investigated.
Yes as you said - if there is not enough progestogen compared to oestrogen on a continuous combined hRT the lining will build and eventually break away by itself.
Dies this clarify? Hopefully not too confusing?
Hurdity x