XL question about PEEK and BASIC on the ROM?

I have an 800XL i believe to be stock, i'm not trouble shooting anything specific just learning more about the machine so have been trying PEEK(xxxxx) commands and non of them work they just return ERROR.

I've tried random numbers and also ones which are meant to return stuff such as 'On an XL/XE PEEK(65527) returns the OS version' Taken from the forum link below.

No matter what number i put in i get ERROR, other features like PRINT FRE(0) work.

Basic things like SETCOLOR work fine. Self test all passes correctly.

I want to know what version of basic is on my machine and also if the version that came on the 800XL ROM was complete, or did people upgrade or overwrite it back in the day?

https://forums.atariage.com/topic/236734-800xl-custom-rom-questions/

Thanks