How we cite our quotes:
No one showed an instant's suspicion that Orlando was not the Orlando they had known. If any doubt there was in the human mind the action of the deer and the dogs would have been enough to dispel it, for the dumb creatures, as is well known, are far better judges both of identity and character than we are. (4.21)
This dovetails nicely with the elevated place nature holds in Orlando. While humans may be fallible and inconstant, nature never is.
How she had loved sound when she was a boy, and thought the volley of tumultuous syllables from the lips the finest of all poetry. Then--it was the effect of Sasha and her disillusionment perhaps--into this high frenzy was let fall some black drop, which turned her rhapsody into sluggishness. […]She had formed here in solitude after her affair with Greene, or tried to form, for Heaven knows these growths are agelong in coming, a spirit capable of resistance. 'I will write,' she had said, 'what I enjoy writing'; and so had scratched out twenty-six volumes. Yet still, for all her travels and adventures and profound thinkings and turnings this way and that, she was only in process of fabrication. (4.27)
This passage first of all demonstrates that Orlando’s encounters with Sasha and Greene were important in the formation of his (or her) identity, and secondly it establishes that the person "Orlando" is still in the process of formation. Orlando’s subjectivity changes constantly.
So then one may sketch her spending her morning in a China robe of ambiguous gender among her books; then receiving a client or two (for she had many scores of suppliants) in the same garment; then she would take a turn in the garden and clip the nut trees--for which knee-breeches were convenient; then she would change into a flowered taffeta which best suited a drive to Richmond and a proposal of marriage from some great nobleman; and so back again to town, where she would don a snuff-coloured gown like a lawyer's and visit the courts to hear how her cases were doing,--for her fortune was wasting hourly and the suits seemed no nearer consummation than they had been a hundred years ago; and so, finally, when night came, she would more often than not become a nobleman complete from head to toe and walk the streets in search of adventure. (4.92)
By dressing as a man, Orlando explores different aspects of her identity. This connects well with the passage earlier in the chapter that argues clothes instead wear (or define) people. By donning different outfits, Orlando gives her different selves a physical manifestation and takes on different identities.