@ppppenguin, thanks a lot, I appreciate the answer! So, if not full-frame TBC, then at least TBCs that would hold several lines could be built relatively cheaply?

I've read that at least one late-1980s VCR had TBC with a window of just one line I think (is it possible? Should not it be longer than a line, at least a line and a half?) which was implemented purely in analog form, no digitizing. I don't know how they would sync up this analog line. I don't think they would fix velocity.

Until you had one-chip line stores and affordable ADCs/DACs even a one line TBC was quite expensive. There was at least one general purpose TBC that used analogue methods. Charge coupled delay chips ISTR. I don't think it was very good.

The very first TBCs used variable analogue delay lines to get a microsecond or so of delay. This was enough to correct monochrome replay of quadruplex VTRs. Imagine a lumped LC delay line with varicap diodes instead of the fixed caps. Plus a compensator to change the termination resistance as you varied the characteristic impedance. Very complex, very expensive, very difficult. Ampex called it AMTEC. The very fine vernier TBC for NTSC/PAL colour replay was called COLORTEC. The Ampex AVR1 quadruplex introduced a one line delay using switched quartz delay lines. All analogue. Again very complex and expensive.

I think only quadruplex VTRs really needed velocity compensation. You only really needed it with direct colour and that was only used in full broadcast grade VTRs such as quadruplex. The delays here were small and implemented with analogue methods.