Assumptions have limited use in science. Ultimately, they hafta be tested against nature, observation, experimental results, etc before a theory can be formulated. Even if radio isotope dating threw up discrepancies within a single sample, there is still a huge disparity between billions of years and a mere few thousand. The film is still of interest regardless, and of course I will consider any evidence I find to the contrary.
While we're on the subject, the Shroud of Turin was dismissed as a 12th C. forgery on the basis of radio carbon dating carried out in 1988. Further investigation since then has found that the actual test sample was part of a repair carried out after it suffered fire damage.......in the 12th C! The repair is distinguished from the original cloth by a different weave pattern, and I believe some scientists have tried to obtain permission from the 'Holy See' to test a piece of the original material.
SInce this would necessarily involve the partial destruction of a prized relic, permission has been refused to date. Not that Christians need such evidence to prove the historicity of the Resurrection (aside from the Gospels themselves, that was more than ably accomplished by Frank Morrison in his brilliant book, 'Who Moved The Stone?'), but if such a test were allowed, it would at least settle the question of its true age, and reopen the possibility that it is the genuine article rather than a medieval fraud.