[Mesorah] malei de malei rule?

[D&E-H Bannett]

Re: <<beis, chaseir d'chaseir bliy' (twice chaseir-chaseir; 
what is "bliy'"?)>>

bliy' stands for b'lishna.  However my mesorah says dalet, 
not bet,  That is, there are four hatovot chaser d'chaser, 
namely Breishit 6:2; twice in 41:26; and Devarim 6:10.

BTW, The subject talks of a rule.  I might have missed 
earlier posts. What is the rule that is involved here.  I 
have often stated on-list that I'm opposed to rules, all I 
know is that sometime a word might appear in different 
places malei, chaser, malei d'malei, etc.  There are even 
words with a letter that  is chaser a letter d'karia v'lo 
ketiva.  Do they have rules?  Isn't the verification by the 
ba'alei Mesora of different spelling of the same word 
sufficient for us to accept their existence and correctness 
in each place that they appear?


David