You're certainly correct about the spacing of "Last Act" (the 3rd episode, if counting DK&DK2 as one; the 4th if not) and "Francesca" (the 3rd-from-last episode as aired; the 2nd-to-last as filmed, due to a miscommunication about Vachon's availability).
And of course you're correct that if writer Gillian Horvath hadn't chosen to expand on this specific "blood knowledge" trope in "Francesca," it would have existed only in "Last Act," and nowhere else in the series. ("Last Knight" would seem to show it exactly backwards, with Nick's own flashbacks instead of Natalie's when he bites her. That caused debate about whether Natalie should be considered to see those images, as she wasn't getting any blood, only losing it. And why was Nick apparently not seeing anything about Natalie from her blood at that pivotal moment? Oh, the budget constraints of clip shows...)
Ms. Horvath worked on both FK and HL, among other TV series, in that era, and she had a strong reputation for two very frequent factors in the episodes she wrote:
hearkening back to earlier content in series canon
introducing supernatural elements not previously present (or present but not explicit) in series canon
"Francesca" certainly hearkens back to "Last Act" with the "blood knowledge" content! And if Francesca in the present day is a ghost possessing Frank, then Francesca's ghost also hearkens back to Erica's ghost as much to the ghosts in Kessel House in "Dead of Night." But if Frank is Francesca reincarnated (instead of possessed), then reincarnation would count as a supernatural element never previously explicit in series canon. Very typical of Ms. Horvath's work, either way.
Re: The flashback
And of course you're correct that if writer Gillian Horvath hadn't chosen to expand on this specific "blood knowledge" trope in "Francesca," it would have existed only in "Last Act," and nowhere else in the series. ("Last Knight" would seem to show it exactly backwards, with Nick's own flashbacks instead of Natalie's when he bites her. That caused debate about whether Natalie should be considered to see those images, as she wasn't getting any blood, only losing it. And why was Nick apparently not seeing anything about Natalie from her blood at that pivotal moment? Oh, the budget constraints of clip shows...)
Ms. Horvath worked on both FK and HL, among other TV series, in that era, and she had a strong reputation for two very frequent factors in the episodes she wrote:
"Francesca" certainly hearkens back to "Last Act" with the "blood knowledge" content! And if Francesca in the present day is a ghost possessing Frank, then Francesca's ghost also hearkens back to Erica's ghost as much to the ghosts in Kessel House in "Dead of Night." But if Frank is Francesca reincarnated (instead of possessed), then reincarnation would count as a supernatural element never previously explicit in series canon. Very typical of Ms. Horvath's work, either way.