Dear Martin and David,One reason this phenomenon is called ārṣa is that it is quite common in the epic texts (the texts of the ṛṣi-s) such as, e.g. your Gītā passage. There are, for example some nine examples in the critical edition (and apparatus) of the Uttarakāṇḍa of the Vālmīkirāmāyaṇa.Best,