Assitance needed with an alleged Knoll Saarinen Tulip table...underside cross hatched membrane?  

I was inspecting a Tulip table reported to be a genuine Saarinen sold by Knoll. The bevel, diameter, and height are all as should be. There are no labels or stickers or plaques on the underside however the seller said Knoll was molded in the underside of the pedestal base. I peeked at the underside to see if there were any BR50 or BR51 stamps (none) but the shop was cramped and a little dim so did not see the Knoll name in the aluminum casting however I did see the center nut for the rod. I now believe the BR codes refer to vintage pieces. As the shop was a little cramped I did not want to go through the process of upending the table with the seller until certain I was willing to make the purchase.
There are three large black phillips type screws, not on the pedestal top, but on the supportive platter between the pedestal and marble. I had read there should never be screws visible on the Knoll tulip tables, but did see photos here of the exact same enhanced attachment this table has, and the Knoll signature plaque is clearly visible in those photos. The discussion included a statement that the oval marble tables had four such screws on the platter.
My question here regards the fact that the underside of the marble top has a cross hatched membrane. The seller stated he had seen this before on Knoll marble tulip tables. As I do not know the seller's reputation I am inquiring if this is common on later Knoll Saarinen tables. Can anyone chime in? It occurred to me it could perhaps be a repair or later reinforcement. Please refer to the attached photo.
The table has a Colombino brown rose marble top which is absolutely beautiful. Everything else about the table seems to check out with being an authentic Knoll product except the lack of the plaque. It is very well made and in great shape, I am guessing it may be '90s production?
Lastly I am curious as to people's opinions on collectibility or value of vintage versus later Knoll tables. I heard,
perhaps incorrectly, that the very latest Knoll Saarinen tables are made in China, can anyone confirm? I believe manufacture was in Italy although perhaps the original vintage '50;s were made in the USA. Personally this will be a period piece in my kitchen used daily and I am less concerned with value, but would like to be as informed as possible.
Thank you in advance for any information you contribute!