Yes you can get D3 invitations to visit and do pre-reads, which turn into offers of slots, from schools who have only seen you at one Headfirst showcase. My son had a PG (tournament) and PBR (showcase) profile, had been at big tournaments, and had attended one HA school's camp, before HF. However, most of the schools who contacted him after HF had not seen him before, nor had he ever contacted them. He had a good showcase, and it was backed up by the other stuff - I'm not sure it would have had the same impact if that were all he had done.
We were flying totally blind, didn't have a clue what he should be doing, and travel coaches did not have much sense of the non-local HA scene. Not from an elite HS, and no-one from his school had done this before.
Btw, only one D3 coach ever reached out to either travel or HS coaches. I always thought that was strange. We did ask travel coaches to contact some D3 coaches, although they did not know them.