Why some of the interfaces are not getting loaded even after NIC card got detected in the system ?

Issue

• System has some onboard cards and some NIC cards added later.
• Below is the lspci output showing all the NIC cards detected.
• Out of these 8 cards, in ifconfig output can see only 6 interfaces got loaded.

~]# grep -i ethernet lspci 
01:00.0 Ethernet controller: Intel Corporation Ethernet Controller 10-Gigabit X540-AT2 (rev 01)
01:00.1 Ethernet controller: Intel Corporation Ethernet Controller 10-Gigabit X540-AT2 (rev 01)
04:00.0 Ethernet controller: Intel Corporation 82599EB 10-Gigabit SFP+ Network Connection (rev 01)
04:00.1 Ethernet controller: Intel Corporation 82599EB 10-Gigabit SFP+ Network Connection (rev 01)
07:00.0 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)
07:00.1 Ethernet controller: Intel Corporation I350 Gigabit Network Connection (rev 01)
43:00.0 Ethernet controller: Intel Corporation Device 1512 (rev 01)
43:00.1 Ethernet controller: Intel Corporation Device 1512 (rev 01)
             +-01.0-[01]--+-00.0  Intel Corporation Ethernet Controller 10-Gigabit X540-AT2
             |            \-00.1  Intel Corporation Ethernet Controller 10-Gigabit X540-AT2
~]#

• As per booting logs from dmesg and /var/log/messages the card for which no interface(ethX/emx/pxpx etc) where seen is Intel Corporation Device 1512 (rev 01