Oh... That's just the start of the trickery. DEC and HP (and the Apple II, in high-res mode) had tricks to shift (delay, really) groups of pixels by half a pixel, giving us better A's and V's, and more rounded O's.
So the HP 2645 did use a half-bit shift and it's quite clever. It's shown in this video[1] by CuriousMarc (I've set the timestamp to the relevant part). The document shown in the video is available on the Internet Archive[2]. It also reminds me of techniques used in Epson dot matrix printer fonts, where the rate of pin firing couldn't be increased, but the half-pixel timing could be.
I'm pretty sure DEC VT100 and VT220 did not do this. There is some dot-stretching logic in the VT100 and VT220[3], which improves appearance but doesn't increase effective resolution.
Apple ][ is a slightly different story. The high bit (very similar to the HP terminal) does cause a half-pixel shift, but I believe this was almost entirely used to create more colors through NTSC artifacts, not to increase horizontal resolution. I'm unaware of a character ROM that uses the technique, but I could be missing something. The best writeup I've found is [4], and I also found an original description in BYTE magazine[5] from Steve Wozniak himself.
Some of those block diagrams were a bit oversimplified. One cannot address 9 rows with only 3 address lines, for example. Or do block graphics with just 4 NOR gates.
