External validation of logistic-based risk in time-to-event setting

These risks come from EMR vendor-proprietary models. I think it was developed simply retrospectively following patients for one year in one healthcare system (ignoring loss to follow-up). I am exploring ways to go about at least evaluate it in our health system. But these risks are calculated and added to patients’ records at each visit, which leads to issues of varying time between visits (and multiple visits and recalculation of the risk within one year itself). The naivest approach for external validation in this case may be to index on one risk (maybe the first) and follow-up for one year for outcomes, ignoring other visits and other estimated risk, and evaluate discrimination/calibration. But this seems inefficient to me, as we are ignoring lots of clinical info from the follow-up.