The reported goof of the final whisker plucked by Uncle Pecos doesn't appear in the Cartoon HQ Triforce version. The last whisker is the top left, which correctly follows the order of the previous whiskers.
After Uncle Pecos' first guitar string broke, the first whisker Uncle Pecos jerked off of Tom was his Tom's bottom right. Second was Tom's top right whisker. Third was Tom's left middle. Fourth was Tom's right middle. Fifth, Tom jerked off of himself, must have been his own left top or left bottom. During Uncle Pecos's singing, the whisker that Uncle Pecos, off of Tom through the television screen, was Tom's right middle whisker, which was the fourth, Uncle Pecos plucked off of Tom, while he was in Tom and Jerry's house.