Around that time frame your vehicle should have a proportioning valve with a pressure differential valve in the center. The purpose of the differential spool valve is to shut off either the front or rear circuits if the brake pressure is not equal on both circuits due to a system failure and prevent a long pedal travel. While normally self-centering, with age they get stuck to one side often while bleeding.

I have a feeling that is what has been happening to you. After the new pads were installed it appears to me the valve shuttled and shut off the rear brakes. This would cause less then ideal performance (no rear brakes) and this is what caused you not to be able to draw fluid from the rear wheel cylinders.

When you pressed on the brake when bleeding you got the valve to shuttle to the opposite direction. Sometimes tapping on the valve will get it to center, or with older vehicles sometimes you have to bleed a little from the opposite axle to get it to center. If you search this site you will find some answers about using a little clip to hold the spool valve in the center position when doing brake bleeding.

That's not to say you aren't correct that a frozen wheel cylinder will give you a higher pedal. It will due to the lower brake fluid volume without the wheel cylinder pistons moving out. Often consumer comments from that is the pedal is high but the vehicle does not stop as well.