I assume you pulled the MX240 specs from the current spec sheet. If so, I would assume that the older EOL RE-S-2000 routing engine that shows only support for 32bit Junos and lower RAM will not be able to have that many resources. Specs for the routing table are highly RAM dependent.
And looking at the overall RE support in the hardware guide, I don't see the per RE specs that would be helpful in this case. With some deeper searches you might be able to turn up the per RE specs. Or this is a good questions for your Juniper sales engineer or partner sales engineer that has better access to internal spec documents.