I was imprecise in my question. I had meant "previous" to mean all Arab immigration previous to the present day, not to distinguish more ancient immigration from more modern. It is irrelevant from which wave of immigration the present Arab population is descended, as if we could even distinguish such in what must be a highly mixed population. The point that I had wanted to make, in answering the question what these two groups have to do with each other, is that the descendants of both groups are now residences in the territory controlled by Israel.
The fact that some Arabs are descendants of a more recent immigration does not delegitimize their presence any more than the fact the the Jewish population is made up of descendant and actual members of a much more recent Jewish immigration. If you are going to discount the modern Arab immigration then you must do the same with the modern Jewish immigration. If anything, the Arab population pre-dates the bulk of the Jewish population.
It is useless for either side to seek to delegitimize the population of the other because of when they arrived. The land has a mixed Jewish and Arab population and neither is going anywhere. Both sides need to accept the population that is present on the ground today.
The recent Arab immigration (late 1800-1945) are not connected to the “900” years you kept mentioning.
In Short, from about 250,000 around the end of the 19th century, many of them bedouins, the Arabic population grew to about 1,250,000 in 1948. The Palestinian claim that they are the ancient population of the so called Palestine has no ground.
Winston Churchil, said in May 22, 1939 that the Arab immigration to Palestine during the British Mandate was so large that their numbers grew in such proportion that even if all Jews immigrated to Palestine they could not reach that number.
Franklin D.Roosevelt, said in May 17, 1939 that the Arab immigration to Palestine since 1921 was much greater that Jewish immigration.
A significant part of the 1948 Palestinian refugees were first or second generation illegal immigrant workers.
Arab Immigration into the Coastal Plains of Israel (the Sharon) During the British Mandate.