I was taught to double-genuflect at any time the Blessed Sacrament was exposed. I was taught that when the Blessed Sacrament was present within the tabernacle to single genuflect. This was done when crossing from one side of the church to the other, upon entering or leaving the sanctuary, upon leaving one’s place in church (if you hadn’t just done it because you just left the sanctuary), and upon first taking a place in church. During Mass, though, all attention was directed to the altar, not the tabernacle. Of course, if you weren’t physically able, you did what you could manage (for instance, I could sometimes only manage a bit of a curtsy if carrying a huge flower arrangement with a full vase).
Our parish wasn’t Tridentine, but I remember cleaning church taking quite a lot of genuflecting.