In this answer https://dinonline.org/2011/06/23/basic-guidelines-for-the-first-night/ point number 4, you write “Even if no bleeding is discerned, if the husband completes marital relations (complete penetration), his wife is prohibited to him, and she must complete the process of purification, though she doesn’t recite a blessing upon immersing in the mikva.” Can you please source this assertion? I understand that separation without bleeding is a somewhat later practice than were there bleeding, but it seems pretty universally accepted. What sources explicitly discuss omitting a blessing on a immersion in that case? (Common custom, as far as I know, is to still yes say a blessing following immersion during Dam Tohar days.)
Rav Ovadia Yosef in his Taharat Habayit [15:3, pg. 542] rules that in deference to the opinions that only with blood does she become a nidah, she would not make a bracha on the tevila. In his opinion this is a case of “safek brachos lehakel”. In fact the Chasam Sofer in his teshuvos [Even Haezer Vol. 1 143] rules that in fact one may make a bracha after penetration alone.
Practically speaking this question is generally not relevant as most brides through scheduling or hormone pills receive their period in the days after the bias mitzvah and hence have the status of a regular niddah by the time of immersion. If one were to be faced with this scenario it would seem that one could in fact make the bracha on the tevila.