I made once a thread about it. ATP includes to player's activity all Davis Cup matches no matter on which level they were played but hasn't included Borg's Davis Cup matches in 1978 to its database, therefore for example on wikipedia
you can read that Borg has the third longest winning streak - 43. In fact he won 49 consecutive matches in 1978 (43 + 6 Davis Cup rubbers), Vilas's 46 is consisted of 44 tournament matches + 2 Davis Cup rubbers.
thanks for the answer
what sounds strange to me is that Vilas's record is very well-known and it was in a time when people didn't put so much their trust in computer data : I have difficulty to imagine that it comes only from a technical error
maybe there's something else which explains that Borg's record was not counted ? matches out of the ATP tour (WCT ?) or whatever ?
anyway Vilas's record was also stopped because of the spaghetti racket then ...