The first member of a tat-puruṣa samāsa preserves its original accent when the second member is the word śārada having any other sense than that of 'autumnal'.,
The word आर्तव means appertaining to season (ऋतु) i. e. when the word शारद does not refer to the season of शरत् or autumn. Thus र꣡ज्जुशारदमुदकम् 'fresh drawn water'. So also दृष꣡त् शारदाः सक्तवः 'the saktu flour fresh from the mill'. The word शारद means here 'fresh' 'new': and it forms an invariable compound. The word रज्जु is formed by उ affix added to सृज् (Unadi I. 15), the स being elided. The affix उ is treated as नित् (Unadi I. 9) and the accent falls on the first syllable 6.1.197. The word दृष꣡त् is formed by the augment ष and shortening of the vowel of the root दृ 'to tear' (दृणाति), and the affix अदिक् (Unadi 1. 131) and has accent on the final 3.1.3.
Why do we say 'when not meaning autumnal'? Observe परमशारद꣡म्, उत्तमशारद꣡म् 'the best autumnal grass &c'. 6.1.223.,