Rawm is not available with every final vowel. It is permitted, subject to its other conditions, with final kasrah and dammah, but not with final fathah. This provides an immediate practical distinction.
Kasrah: the final nun of «الْعَالَمِينَ» can receive a very slight audible trace of its underlying kasrah.
Dammah: the final nun of «نَسْتَعِينُ» can receive a similarly faint portion of its dammah.
Fathah: this method of stopping is not used for an ordinary final fathah.
Yet the surface vowel mark is not the only question. Later we will distinguish temporary vowels inserted for phonetic convenience. Such a vowel may appear in connected reading without permitting rawm at a stop.