Dear Ziad,
Of course a visit number is interresting... if you want visualize your data and order it by visit number. Having a visit number at your paper forms is also interresting for the very same reason.
However, most analysis softwares such as R and Stata do not bother with the visit number while running survival analysis - which I guess you will do later. :) For survival analysis the most important data is the date of the evaluation, somehting indicatig what happened at the period, and a date indicating the beggining of the period. Most softwares have available analysis whith time dpending variables - which has a dataset wiht a structure containing the same patient at several lines - each line a different period. Of course to do that, there must a unique idenfier for each patient which will be repeated all the lines where the same patient appear.
Again, visit number is important but not that importatn. As a previous answered, if you already started your job and you have a lot of data in your dataset it will be easier to insert a variable indicating visit number. Otherwise, you could update you qes file with a nwe variable indicating visit number.
Best regards, Pedro Emmanuel