When a Moviestock delists, all the Starbonds attached to that stock are adjusted in price to match their new TAG.
For an example coming up this week, JKNOX's last five movies grossed about $200 million total. Dividing that figure by five to come up with an average, we get a TAG of $39.89 million.
On Monday, after JCKA3 delists, JKNOX's TAG will drop the oldest movie in his current TAG DGTWN (which grossed $11 million) and add JCKA3, which has grossed about $111 million.
With DGTWN out and JCKA3 in, the total box office of JKNOX's last five movies is now $300 million, so the TAG will be adjusted on Monday evening to about $60 million.
On Tuesday afternoon, JKNOX's price will be adjusted to H$60, to reflect the new TAG. Since JKNOX is currently trading at $55, investing in his Starbond now will net you $5 profit per JKNOX bond you hold ($100K if you hold a max position).
If a movie star has been in fewer than five movies, the TAG is calculated differently. If the Starbond has four credits, to get the TAG you divide the total box office by 4. If the Starbond has three or fewer credits, the total box office is divided by 3.
That's how they work - and the point of them is, to make money :)