What I Feel Qualifies as a Valid QSO on the Digital Modes

If I send you a signal report and receive a signal report in reply (or vice versa), I log the contact. I could find nothing in the ARRL rules stating you have to exchange 73's to make it a valid QSO, just callsigns and signal reports. In the September 2018 issue of QST, Joe Taylor, K1JT, stated, "If you have received RRR that is, a definite acknowledgment of all of your information and your QSO is officially complete." If we exchange 73's, wonderful, it is nice to be cordial and wish each other well or further confirm the contact with 73's and as a rule I will always attempt to do just that, but I will also log QSOs with just signal reports.