CCS/AWR1843BOOST: compatibility between labs for AWR1642 and AWR1843

Tool/software: Code Composer Studio

Hi, a time ago I asked a similar question in this forum

then you told me that the labs between boards are compatible, so all this time I have been working in my AWR1843BOOST EVK with no issues with source code from CCS rebuilding and loading labs for AWR1642 or AWR1843 in debug and deployment mode

But now I am having issues flashing binaries using source code from CCS for a custom awr1843 board (only works flashing the MRR or MRR steering lab) so I was searching info in the forum and here you say this:

"You may need rebuild the application while selecting AWR1843 device in CCS project properties setting"

and here you say this:

"An application written for AWR1642 will run on AWR1843 without recompiling as long as the adjustment is made in the chirp config file to use Tx antennas 1 and 3 verses antennas 1 and 2 on the 1642.  If you want to port/rebuild the application from 1642->1843, two things must change:

1) the pinmux statements that configure UART, SPI, CAN, etc.  These are usually done in the MSS, and should be wrapped in #ifdef SOC_XWR18XX ...  #endif statements.

2) SOC_XWR18XX will need to be defined for both MSS and DSS builds instead of SOC_XWR16XX "

So now I am confused, why do you say I need this extra steps to run a lab made for AWR1642 in the AWR1843?, in my EVK I never needed this steps, do I need to do this for a custom board?, somehow the AWR1843BOOST EVK firmware knows that an AWR1642 code is being loaded and allows that kind of config?

thanks