I have an old 27" standard def tube TV. We have analog cable. Recently, within the past 6 months I'd say, some stations are cut off on the edges. Most notably, one of the PBS stations is like this. There are 2 PBS stations, I guess one is the national feed and one local? It's really noticeable on one of them, about half the letters are cutoff on some of the fonts.

It may be my imagination, but I think I noticed this around the same time that the US was supposed to switch to OTA HD and then the date got pushed back. I know I have cable, but I thought there might be some correlation.

I'd say it's the PBS station, unless you see it on all stations. My local PBS does fun things with the standard def channel: small picture centered in screen (from HD downconversion), very small picture centered in screen, normal letterbox, etc. More erratic than any other channel.

If the station has already converted to digital, it is now either an HD or SD digital signal. The cableco must then convert it back to an SD analog signal for distribution. An HD signal needs to be center cropped, down converted and converted to analog while an SD signal needs just digital to analog conversion. Either way there is hardware at the cablco headend that performs this function. That component coupled with the issues raised by jdre above, could be the problem. I doubt you can do anything about it on your end.