@pimoa you can use underLabel option of Single Value visualization to add a caption with token which can have value of Year To Date value using an independent search.
Following is a run anywhere example based on Splunk's _internal index which runs an independent search to pull current year count and uses <progress> search event handler to set the token for total count for Year to Date. Then the same token is used in Single Value with underLabel .
<dashboard>
<label>Single Value with Trend and Additional Info</label>
<!-- Search Query for Year To Date Data -->
<search>
<query>| tstats count where index=_internal earliest=@y</query>
<earliest>-24h@h</earliest>
<latest>now</latest>
<sampleRatio>1</sampleRatio>
<progress>
<set token="tokYearToDate">$result.count$</set>
</progress>
</search>
<row>
<panel>
<single>
<search>
<query>| tstats count where index=_internal earliest=-30d by _time span=1d</query>
<earliest>-24h@h</earliest>
<latest>now</latest>
<sampleRatio>1</sampleRatio>
</search>
<option name="colorBy">trend</option>
<option name="colorMode">none</option>
<option name="drilldown">none</option>
<option name="numberPrecision">0</option>
<option name="rangeColors">["0x53a051","0x0877a6","0xf8be34","0xf1813f","0xdc4e41"]</option>
<option name="rangeValues">[0,30,70,100]</option>
<option name="showSparkline">1</option>
<option name="showTrendIndicator">1</option>
<option name="trellis.enabled">0</option>
<option name="trellis.scales.shared">1</option>
<option name="trellis.size">medium</option>
<option name="trendColorInterpretation">standard</option>
<option name="trendDisplayMode">absolute</option>
<option name="underLabel">$tokYearToDate$ (YTD)</option>
<option name="unitPosition">after</option>
<option name="useColors">1</option>
<option name="useThousandSeparators">1</option>
</single>
</panel>
</row>
</dashboard>
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