Ok, to be sure that we understand each other...

My Sub2_CA_entire_chain.pem looks like this:

-----BEGIN CERTIFICATE-----
XXXXXXXXXXXXXXXXXXXXXXXXXX
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
YYYYYYYYYYYYYYYYYYYYYYYYYYYYY
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
ZZZZZZZZZZZZZZZZZZZZZZZZZZ
-----END CERTIFICATE-----

where XXXXXXXXXXXXXXXXXXXXXX is Root_CA certificate,
YYYYYYYYYYYYYYYYYYYYYYYYYYYYY is Sub1_CA certificate and
ZZZZZZZZZZZZZZZZZZZZZZZZZZ is Sub2_CA certificate.


For me this a certificate chain which in that special case equals
concatenated file. Am I correct?