Yehoshua Zimri / יהושע זמרי [earliest recorded ancestor of RASHI] - 20 generations without a name?

How do you know, that Hassandlar was an ancestor of Zimri (who is actually the oldest recorded ancestor of Rashi)?

And how do you know, that there are 20 generations between Hassandlar and Zimri? I guess, this is just speculation...

At this time there is stated on Zimris main page:

"Traditionally - TWENTY THIRD GENERATION progeny of Yokhanan haSandlar?, although a gap of ca. 900 years would span more than 23 generations."

I don't know, what is meant with 900 years? As far as I can see, Ya'akov ben Shlomo is born ca 75, this is 965 years before Rashi and there are more then 30 generations between them, even without additonal 20 mystical Hassandlar-generations (without a name).

The average time for a generation in jewish scholars is 30-35 years, you can see this typical time span as well in the time from David to Ya'akov ben Shlomo (1000 years for 30 generations), and again there are 970 years needed for the 28 generations from Rashi to present time.

this means even if Zimri was the son of Hassandlar, we have already a relatively short time to fit in all generations. If needed we can calculate together more precisely, but I can already say for sure, that there is absolutely no space for 20 or more additional generations, to fill a virtual gap (which isn't existing!).

So my question is: is Zimri really related to Hassandlar? And when (how do you know?) how are they really related?