First column:   year   month .   Number of months
Repeat day codes every columns.   Entry padding em.  

202520252025202520262026
SepOctNovDecJanFeb
      
Mo1Mo1Mo
Tu2Tu2Tu
We31We3We
Th42Th41Th
Fr53Fr52Fr
Sa641Sa63Sa
Su752Su741Su
      
Mo863Mo852Mo
Tu974Tu963Tu
We1085We1074We
Th1196Th1185Th
Fr12107Fr1296Fr
Sa13118Sa13107Sa
Su14129Su14118Su
      
Mo151310Mo15129Mo
Tu161411Tu161310Tu
We171512We171411We
Th181613Th181512Th
Fr191714Fr191613Fr
Sa201815Sa201714Sa
Su211916Su211815Su
      
Mo222017Mo221916Mo
Tu232118Tu232017Tu
We242219We242118We
Th252320Th252219Th
Fr262421Fr262320Fr
Sa272522Sa272421Sa
Su282623Su282522Su
      
Mo292724Mo292623Mo
Tu302825Tu302724Tu
We2926We312825We
Th3027Th2926Th
Fr3128Fr3027Fr
Sa29Sa3128Sa
Su30SuSu

35 rows

Notes on curious non-bug on my home machine:
with date_default_timezone_set('UTC') - be patient
without that declaration