Master MOS Y2K in OSWORD 14
                     ===========================

The only part of the Master MOS that does anything with centuries is the
string returned by OSWORD 14,0. It is hard-wired to 19xx. Code calling
OSWORD 14,0 should always be checking the returned result anyway in case
there is no RTC at all, with something like:

  X%,Y%=>control block
  A%=14:?X%=0:CALL &FFF1
  T$="":IF ?X%:X%?24=13:T$=LEFT$($X%,11)+STR$(26-(X%?13)DIV8)+$(X%+13)
  REM T$="" if no RTC, else T$=time string with correct century

There's enough space in MOS 3.20 and MOS 3.50 to squeeze in a full 19xx vs
20xx year check, but - the further into the 21st century we get, the more
remote is the need for OSWORD 14 on live hardware to return the year as
19xx, so why not hard-wire it to 20xx.

This is easily done with:

MOS 3.20: 9881 change to &20
MOS 3.50: 9664 change to &20

However, if you do want to patch the MOS to return both 19xx and 20xx, it
can be done with:

Patch MOS 3.20
--------------
9880: C9 38    CMP #&38  ; Compare decade  <- was: 9880: LDA #&19  ; Century=19
9882: 20 DF B8 JSR &B8DF ; Call patch      <- was: 9882: JSR &9893 ; Insert century

B8DF: A9 19    LDA #&19  ; Prepare century=19
B8E1: B0 02    BCS &BEE5 ; Decade>='8', use it
B8E3: A9 20    LDA #&20  ; Set to century=20
BEE5: 4C 93 98 JMP &9893 ; Insert it and return

Patch MOS 3.50
--------------
9663: C9 38    CMP #&38  ; Compare decade  <- was: 9663: LDA #&19  ; Century=19
9665: 20 21 FB JSR &FB21 ; Call patch      <- was: 9665: JSR L9676 ; Insert century

FB21: A9 19    LDA #&19  ; Prepare century=19
FB23: B0 02    BCS &FB2C ; Decade>='8', use it
FB25: A9 20    LDA #&20  ; Set to century=20
FB27: 4C 76 96 JMP &9676 ; Insert it and return