Natural England  only accept “negative” eDNA results for newt licencing where efficacy has been proven ( e.g. between the above dates and by trained personnel ) . “Positive” results clearly have no such limitation.
The pilot work  on using eDNA for detecting newts relied on comparing conventional field survey techniques to eDNA and comparative results were therefore only available during their sampling period i.e. mid-April and late June. Detection rates for sites where newts were known to be present were 99.3% using professionals and 91.2% using volunteers.
The report [ 2 ] states that “Overall, collecting eDNA appears to be a highly effective method for determining whether Great Crested Newts are present or absent during the breeding season. We do not know how effective the method is outside this period.”
Natural England indicates the peak season for surveying for larvae is August, so in theory these should be detected by later eDNA tests.
eDNA declined rapidly once great crested newts were removed from experimental ponds  – to undetectable levels over 1-2 weeks. Ponds could therefore have been utilised by adults earlier in the season e.g. for foraging, but the absence of larvae would point towards absence of successful breeding.
 Biggs, J., Ewald, N., Valentini, A., Gaboriaud, C., Griffiths, R.A., Foster, J., Wilkinson, J., Arnett, A., Williams, P. and Dunn, F., 2014. Analytical and methodological development for improved surveillance of the Great Crested Newt. Defra Project WC1067. Freshwater Habitats Trust: Oxford. http://randd.defra.gov.uk/Default.aspx?Menu=Menu&Module=More&Location=None&ProjectID=18650&FromSearch=Y&Publisher=1&SearchText=wc1067&SortString=ProjectCode&SortOrder=Asc&Paging=10#Description
 Thomsen, P., Kielgast, J.O.S., Iversen, L.L., Wiuf, C., Rasmussen, M., Gilbert, M.T.P., Orlando, L. and Willerslev, E., 2012. Monitoring endangered freshwater biodiversity using environmental DNA. Molecular ecology, 21(11), pp.2565-2573.