Revelation 7:4 states in relation to the 144,000
Then I heard the number of those who were sealed: 144,000 from all the tribes of Israel.Then I heard the number of those who were sealed: 144,000 from all the tribes of Israel.
Revelation 7:9 states regarding the great crowd
After this I looked, and there before me was a great multitude that no one could count, from every nation, tribe, people and language, standing before the throne and before the Lamb
John in this vision only heard the number sealed as being 144,000 and from which tribes of Israel they came from (being 12,000 out of 12 tribes of Israel but if Israel here means mankind in general then what do the individual tribes represent?) He did not see them at this stage.
After John heard the number he then states that he saw a great multitude which no man could number. If we saw a crowd of 144,000 we would not be able to count them either, we would have to set up some type of procedure in order to do this but just by looking at that many people it would be beyond us to count them.
This suggests that it was most likely the same group.