EtherType

That value was chosen because the maximum length (MTU) of the data field of an Ethernet 802.3 frame is 1500 bytes and 1536 is equivalent to the number 600 in the hexadecimal numeral system.

The payload following includes a 16-bit tag control identifier (TCI) followed by an Ethernet frame beginning with a second (original) EtherType field for consumption by end stations.

The proposition to resolve this conflict was to substitute the special EtherType value 0x8870 when a length would otherwise be used.

The draft authors also responded to the chair's letter, but no subsequent answer from the IEEE 802.3 has been recorded.

EtherTypes are assigned by the IEEE Registration Authority,[5] which publishes them in list format.

An Ethernet frame including the EtherType field. Each lower slot designates an octet; the EtherType is two octets long.
Insertion of the 802.1Q VLAN tag (four octets) into an Ethernet-II frame, with a typical VLAN arrangement of a tag protocol identifier (TPID) EtherType value of 0x8100. A QinQ arrangement would add another four-octet tag containing a two-octet TPID using various EtherType values.