Dear list members,

Victor Davella wrote: 

. . .according to the standards as reported in sources spanning some 1600 years and very much still current today, it is absolutely necessary to adhere to grammatically correct Sanskrit and the rules of meter  . . .

It also seems that earlier there wasn't so much a concern.
Of the 12 Gayatri mantras at  Maitrāyaṇī-Saṃhitā  2-9-1, three of those gayatri mantras have extra syllables. 

And see this post of Madhav's http://list.indology.info/pipermail/indology_list.indology.info/2015-January/040590.html  which concludes:  the Brāhmaṇa texts were not bothered by deviations of meters up to two syllables".

Why the change in attitude towards meter?

Harry Spier

tat puruṣāya vidmahe mahādevāya dhīmahi /
     tan no rudraḥ pracodayāt //

     tad gāṅgaucyāya vidmahe girisutāya dhīmahi /
     tan no gaurī pracodayāt //

     tat kumārāya vidmahe kārttikeyāya dhīmahi /
     tan naḥ skandaḥ pracodayāt //

     tat karāṭāya vidmahe hastimukhāya dhīmahi /
     tan no dantī pracodayāt //

     tac caturmukhāya vidmahe padmāsanāya dhīmahi /
     tan no brahmā pracodayāt //

     tat keśavāya vidmahe nārāyaṇāya dhīmahi /
     tan no viṣṇuḥ pracodayat //

     tad bhāskarāya vidmahe prabhākarāya dhīmahi /
     tan no bhānuḥ pracodayāt //

     tat somarājāya vidmahe mahārājāya dhīmahi /
     tan naś candraḥ pracodayāt //

     taj jvalanāya vidmahe vaiśvānarāya dhīmahi /
     tan no vahniḥ pracodayāt //

     tat tyajapāya vidmahe mahājapāya dhīmahi /
     tan no dhyānaḥ pracodayāt //

     tat paramātmāya vidmahe vainateyāya dhīmahi /
     tan naḥ sṛṣṭiḥ pracodayāt //MS_2,9.1//


and see this