I don't know if you consider it an acceptable idea to provide a made up an in universe explanation for something, that might have been either an error, or a conscious decision made for unknown reasons by a person not available to comment, but how about inventing an origin story for this name, summarising it in a sentence or two in a sourcebook, or some other official fiction, and then making sure it gets mentioned on Sarna site in their article about Wrociaw? This should shut up malcontents like me. I'm afraid that until an explanation like this happens, any Pole as well as anyone else with a fair grasp of Central European geography will think it is a typo, and threads like this will pop up from time to time.
Here are a few possible explanations I've just made up:
1. There is a famous work of art (for example a photograph, a dairy, a novel or a painting) in Battletech universe, which shows or describes a scene of total destruction (a battlefield for example) during the Second Soviet Civil War. A central piece of the scene is a signpost which despite is untouched except for a single hole in the middle of a word Wrocław, making it look like Wrociaw. During the era of early space colonisation this work became a famous allegory of the horrors of war, and the name of the planet is a reference to this work.
2. At some point during early space colonisation Polish language got mixed up with some other language (most likely non-Slavic), the way Japanese and Swedish gave birth to Swedenese. Wrociaw is just the name of Wroclaw in that language. Later this language became extinct or just so rare, that it is almost never mentioned in the universe (explaining, why it is never mentioned in the official BT books), and Wrociaw is just the last remaining artefact of the language from the times, when it was popular enough to have planets named with words from it.
3. Wrociaw is a name of some person famous around the time the planet was named. For example someone who died a hero in the first days of interstellar travel repairing some critical damage, that otherwise would kill everyone on ship or new planetary outpost they were at, and by doing so became one of the first people who died outside of the Solar System. Who cares, that such name probably does not exist in real world? New surnames get created from time to time or get misspelled in official papers from time to time (for example by immigration officers, who don't know the language the name is from, or by the migrants themselves, who prefer a spelling, that will result in a more or less correct pronunciation of their names, by most people in the country they moved to).
4. Wrociaw is an extraterrestrial animal, which was named after it's distinctive cry, which to it's discoverers sounded like this word, and the planet is named after the animal.
If you decide to follow my suggestion, take whichever story you want, or use them as an inspiration to make another one. I personally prefer the first two stories, because they can also be used as an in-universe explanation why planet Wrociaw is spelled Wroclaw in some books.
