I believe they are trying to accomplish too much in too few of words.
The basic rule for Lend-Lease Supply Path: “Lender’s Major Factory to Receiver’s Home Country.”
Since as you mentioned, FEC is not Home Country it cannot receive Lend-Lease.
Also, FEC’s Capital is technically London, so its Capital cannot be captured.
To compensate for this, the game designers added the exception “The FEC capital is Calcutta for purposes of tracing lend-lease and capture of enemy capitals.”
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 FEC’s Capital.
IMO, the Rule should be written as “Calcutta is FEC Home Country for purposes of tracing lend-lease, and the FEC Capital for purposes of capture of enemy capitals.”
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.