It was my understanding that ALL late Tiger I tanks had zimmerit and only the very early ones were void of it:

Production of the Tiger I began in August 1942, and 1,355 were built by August 1944 when production ceased. Production started at a rate of 25 per month and peaked in April 1944 at 104 per month. Strength peaked at 671 on 1 July 1944. Generally speaking, it took about twice as long to build a PzKpfw VI than another German tank of the period. When the improved PzKw VI Ausf B Tiger II began production in January 1944, the Tiger I was soon phased out.

I read in The Modeler's Guide To The Tiger Tank that Tamiya's Polyester Putty is another good choice to use as zimmerit. It is a very slow setting putty (depending on your ratio of the supplied hardener) and I've used it before and seams to be an easy one to be patient with.

Steve Patton from SCAT does zimmerit very well and he might be one to ask his method.