I believe they are trying to accomplish too much in too few of words.
The basic rule for Lend-Lease Supply Path: āLenderās Major Factory to Receiverās Home Country.ā
Since as you mentioned, FEC is not Home Country it cannot receive Lend-Lease.
Also, FECās Capital is technically London, so its Capital cannot be captured.
To compensate for this, the game designers added the exception āThe FEC capital is Calcutta for purposes of tracing lend-lease and capture of enemy capitals.ā
Meaning that for the FEC Calcutta is duel purpose acting as Home Country in terms of Lend-Lease only, and as their Capital in terms of capturing FECās Capital.
IMO, the Rule should be written as āCalcutta is FEC Home Country for purposes of tracing lend-lease, and the FEC Capital for purposes of capture of enemy capitals.ā
But to answer your question, the lend-lease to FEC ENDS in Calcutta.
As in normal Lend-Lease rules, if the shortest path of Lend-Lease goes through another Indian Port, then along undamaged railroads to Calcutta, then yes it can go through that Indian port.