One of the boats that he had been using was refurbished by another company and became the newer version of the Delfin.
But since that time, many more ships have appeared and it's really hard to keep up with what is going on. Several large U.S. and European companies like to charter boats so that they can offer fixed departure dates for their clients at special rates. That is fine until there are not enough departure dates available on a particular boat and so the companies have to find another boat that can accommodate their needs. That is one reason why a company might promote one boat on their departures one year, and then a different boat the next year. That is the case with the Amatista. Or if a boat gets "old and tired", the company might decide that they need to switch boats. The La Estrella Amazonica is an example of a new boat that resulted from that scenario.
Changes in ownership can affect things too. For instance a husband and wife owned a company that had two boats. They got a divorce and the wife got the boats, but she did not know how to operate the business, so the company has since suffered.
So, if you have been doing some research because you want to do an Amazon cruise and are confused. Maybe some of those things I mentioned are contributing to your confusion. But at least you have plenty of options to choose from. And more are on the way. Meanwhile, another boat that was supposed to start doing cruises to the Brazilian/Colombian/Peruvian border ran into problems and has not started and the future of another boat that had been operating for a year or two is uncertain because it's parent company is in bankruptcy proceedings. Another company might take it over, but it all depends on the court proceedings.
As you can see, the Peruvian cruise scene is ever-changing. A new one is starting as soon as the Peruvian borders open up in 2020.