The initial experience is indeed saving in the new covenantThe question is whether the Pentecost event is the same kind of thing. If it is, I stand corrected. But the way the Holy Spirit works with an individual and a group of believers is different.
If an entire group 'receives the Holy Spirit'.. that doesn't always mean getting saved. When an individual is 'filled with the Holy Spirit' .. this doesn't usually mean getting saved.
If you see 'them, they, we'... then the subject is the whole group. For eg.. in Acts 19..Paul seeing disciples of Apollos, who had believed. He asks them if they have received the Holy Ghost. They said they don' t know if there be a Holy Ghost.. Paul asks about their baptism also.. but not about their salvation. Not receiving the Holy Spirit as a whole group does not mean they haven't already been saved. These are disciples who believed.
Apollos was mighty in the scriptures, but he didn't know the right way of baptism. They were re-baptised the right way.
About Apollos and the disciples who Paul saw:
Act 18:27 And when he was disposed to pass into Achaia, the brethren wrote, exhorting the disciples to receive him: who, when he was come, helped them much which had believed through grace:
(Act 19:1) And it came to pass, that, while Apollos was at Corinth, Paul having passed through the upper coasts came to Ephesus: and finding certain disciples, (same group Apollos was with)
(Act 19:2) He said unto them, Have ye received the Holy Ghost since ye believed? And they said unto him, We have not so much as heard whether there be any Holy Ghost.
(Act 19:3) And he said unto them, Unto what then were ye baptized? And they said, Unto John's baptism. (Paul is not asking about their salvation)
(Act 19:4) Then said Paul, John verily baptized with the baptism of repentance, saying unto the people, that they should believe on him which should come after him, that is, on Christ Jesus.
(Act 19:5) When they heard this, they were baptized in the name of the Lord Jesus.
(Act 19:6) And when Paul had laid his hands upon them, the Holy Ghost came on them; and they spake with tongues, and prophesied.
The Holy Spirit coming 'on' a group, is not an individual receiving eternal life.
1 Corinthians 12:13 (NASB 2020) — 13 For by one Spirit we were all baptized into one body, whether Jews or Greeks, whether slaves or free, and we were all made to drink of one Spirit.
In the verse you quote
(Act 19:4) Then said Paul, John verily baptized with the baptism of repentance, saying unto the people, that they should believe on him which should come after him, that is, on Christ Jesus.
(Act 19:5) When they heard this, they were baptized in the name of the Lord Jesus.
(Act 19:6) And when Paul had laid his hands upon them, the Holy Ghost came on them; and they spake with tongues, and prophesied.
There is no evidence they had previously believe on Christ'
further it appears they were disciples of John