1000Base-LX or SX Output and Input Requirement Standard
I think you missed an important figure of the Ethernet Standard about the 1000Base-X part:



This figure explains many things:


A PHY is composed of three parts: PCS (Physical Coding Sublayer), then PMA (Physical Medium Attachment) and finally the PMD (Physical Medium Dependent) part.
In case of 1000Base-X, this term "Base-X" is used to cover to three type of "physical" medium: 1000Base-LX, 1000Base-SX and 1000Base-CX, but as these medium share a common PCS and PMA, and their specifics PMD are quite similar, a common name is used: 1000Base-X.


As a reminder:


1000Base-LX and SX: long wavelength (LX) and short wavelength (SX) laser, so optical fiber
1000Base-CX: short-haul copper, usually a coax cable.


So you need to figure out which 1000Base-X medium you are using and just have to look to the appropriate section in the standard (802.3 Standard part 3)


Section 38 for 1000Base-LX and SX
Section 39 for 1000Base-CX