First of all, you should not judge by Chinese transliteration. Because Manchu names are first of all one (or two) meaningful words written together in Manchu; Secondly, even if you look at transliteration, not everyone's name is the rule you said. For example, Little Shenyang's son's name is Feng?enyende, which is a far away from it.
Small Shenyang hexene means "outline and boundary" in Manchu, while Feng?enyende is two words, which probably means Lu Qing residents.
Therefore, from the perspective of Chinese transliteration, the first word can be regarded as the upper word; But in Manchu, it is just a syllable and has no meaning. So it can't be counted as a surname.
Manchu people are used to saying their first names instead of their surnames. They usually don't mention their last names, only their first names. Therefore, many people feel that it is strange that Manchu people have no surname or Manchu names according to China people's habits, but in fact they just have different habits.
Most modern Manchu people use Han surnames. When these Han surnames were changed in those years, some of them were changed according to the old surnames (for example, Hershey might change his surname). There is also the first transliteration based on Manchu names-perhaps the modern part can barely be regarded as a surname.