Refractive Index (RI) variation with Temperature & disagreement between two standards
The refractive index of a pure liquid varies with the wavelength of the light (this dispersion causes the splitting of white light into rainbow colours) and with the density and thus temperature of the liquid (this causes the schlieren patterns when heating a liquid on a hot plate).

The section “Index of Refraction of Liquids for Calibration Purposes”, in CRC Handbook of Chemistry and Physics, 90th Edition (CD-ROM Version 2010), David R. Lide, ed., CRC Press/Taylor and Francis, Boca Raton, FL. lists values for several organic liquids at various wavelengths and temperatures.

Reference values close to the values given in the question can be found for toluene:

$$\textbf{Index of refraction of toluene}\\
\begin{array}{lll}
\hline
&amp;\lambda/\mathrm{nm} &amp;T=20\ \mathrm{^\circ C} &amp;T=25\ \mathrm{^\circ C} &amp;T=30\ \mathrm{^\circ C} \\
\hline
&amp;667.81 &amp;1.49180 &amp;1.48903 &amp;1.48619 \\
&amp;656.28 &amp;1.49243 &amp;1.48966 &amp;1.48682 \\
&amp;589.26 &amp;1.49693 &amp;1.49413 &amp;1.49126 \\
&amp;546.07 &amp;1.50086 &amp;1.49803 &amp;1.49514 \\
&amp;501.57 &amp;1.50620 &amp;1.50334 &amp;1.50041 \\
&amp;486.13 &amp;1.50847 &amp;1.50559 &amp;1.50265 \\
&amp;435.83 &amp;1.51800 &amp;1.51506 &amp;1.51206 \\
\hline
\end{array}$$

The uncertainty of the refractive index is estimated as $\pm0.00003$.

For example, the refractive index measured for toluene using the characteristic wavelength of a sodium-vapour lamp $(\lambda\approx589\ \mathrm{nm})$ at $T=20\ \mathrm{^\circ C}$ is $1.49693$. When increasing the temperature, the refractive index is decreased to $1.49413$ $(-0.19\ \%)$ at $T=25\ \mathrm{^\circ C}$ and to $1.49126$ $(-0.38\ \%)$ at $T=30\ \mathrm{^\circ C}$.

The range of values given in the question corresponds to a decrease between $-0.26\ \%$ and $-0.52\ \%$ when the temperature is increased from $T=20\ \mathrm{^\circ C}$ to $T=27\ \mathrm{^\circ C}$.