"based on the fact that my spleen is not enlarged, can I conclude that my platelet count being on the lower range is not due to liver disease? "
Your platelet counts are as you say within the normal range. Which is just that, "normal". It does
n't get any better than normal.
Your platelet counts are all (except one slightly lower 147 which is mean
ingless) are all within the normal range. 150,000 - 450,000 typically at most labs.