Documentation – Portfolio Visualizer

Sometimes a portfolio model can contain assets with a relatively short history, e.g., new ETFs with a recent inception date. To extend the available data for the portfolio model analysis you can map assets with a short history to their closest proxy, such as the tracked index or a similar passive index fund, which is then used to backfill the asset returns. for the longer time period.

https://www.portfoliovisualizer.com/faq