QSO validity, eg for digital contacts

[VK4ABW]

At what point in a QSO should it be considered valid - eg for QSL purposes ?

On SSB, you exchange and log callsigns and signal reports, maybe other info like name and QTH, then one or both says 73. If you didn't copy something important then you ask for a repeat then say QSL. QSO considered valid and QSL cards might be or are exchanged.

On digital modes, for example FT8 or FT4, the callsigns are exchanged, the SNR is exchanged, maybe grid squares if one station was calling CQ and the other responded in TX1 (rather than TX2). If the SNR wasn't received properly then one side sends the same sequence data again until it is properly decoded before progressing. (That is the equivalent of the speech term QSL.) If the return sequence was RR73 rather than effectively a repeat request then it can finish the QSO, save the details to log.  Does the lack of one or both grid details make the contact incomplete ?

So here is the question : does each station have to receive an actual 73 to consider the QSO finished ?

The purist may say yes but in practice, the answer is no.  Provided the callsigns, reports are exchanged then the necessary data which includes date, time, frequency and mode is available for logging.  The RR73 or RRR in digital simply means all needed data is to hand and this is recognised at the far end by sending a 73 code.

There doesn't need to be anything else.

There has to be a RRR or a 73's or else how do you know the other station got your snr or you got his snr?