Trivia: When Buzz and Featheringhamstan fall after Hawthorne shoots the vine they were stuck on, you can hear a Wilhelm scream.
Trivia: Spoilers! In addition to the mid-credits scene with Captain Burnside, there are actually two post-credits scenes. A humorous scene right after the final credits scroll. Then, about 30 seconds later, right after the Pixar company logo plays, there an extra brief scene involving Zurg.
Trivia: Spoiler! There is a mid-credits scene with Commander Burnside. He is complimenting his space shield that also zaps giant bugs.
Answer: While he would have been "introduced" to her prior to the last voyage, it was the same way that the current Buzz was introduced to her. Through the video that Hawthorne left him. Old Buzz didn't get to know Izzy the same way current Buzz did. Because of that, he just wanted to complete his original mission. He didn't care that his best friend was able to move on and have a family, he just wanted to get everyone home even though they had all moved on.