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

I would like to explore background issues first. For a binary logistic model to work in the first place, no patient could have been lost to follow-up before one year. Is that definitely the case? Second, binary logistic models are very inefficient in this setting, and freeze the user to use only a one-year prognostic horizon. Time-to-event models would have allowed prognostication about any time frame that was within the study’s follow-up window. They would have also handled variable censoring times.