Ui_template doesn't show old data

I've been playing with Plotly once more, and now managed to draw a chart using a ui_template node which accepts injected random numbers being fed into it, and ensures that older datapoints are removed (I can set the number of datapoints in plot), pretty much like the ui_chart (chart.js) node does.
But, whenever the browser initially connects, or the browser is refreshed, the chart clears & starts printing datapoints from that point onwards, and all of the preceding data is not shown.
I can understand why that should happen within a ui_template node, but is there a way around it?

the template can optionally save the last date sent to it... but for a chart that is tricky as that means you would have to either send all the data a one blob - so that it has all the data to re-plot - or you have to cache the data points yourself and resend them on a reconnection.

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