What is the limit of pitching on a cake

I have two meads in a row going and am about to do a third. I used a smack pack for the first batch... I racked to a secondary and then literally dropped must onto the cake in the primary.. I'm about to transfer into a secondary and drop more must onto the cake... My question is that I want to have 20 gallons total of mead making its way to drinkable by november and december. Is there a limit as to how many times I can pitch upon a cake left behind?

I'm not sure about mead but 2 or 3 times seems to be acceptable for beer.

I've used a smack pack 4 times doing exactly what you are doing - racking directly onto the cake. After the 4th use, there was so much yeast, it took way longer for that brew to mellow. It tasted like liquid yeast for about a month after conditioning. Of course, these were all beers.
I will do it again, but after the third, will pour some of the cake off so I don't over-pitch.