I did some reading of...

I did some reading of https://www.spglobal.com/spdji/en/documents/methodologies/methodology-sp-asx-australian-indices.pdf

page 13 contains this "The following buffers aim to limit the level of index turnover that may take place at each quarterly rebalancing, maximizing the efficiency and limiting the cost associated with holding the index portfolio.Rank Buffer for Index Addition DeletionS&P/ASX 20 14th or higher 26th or lower ; S&P/ASX 50 39th or higher 61st or lower; S&P/ASX 100 84th or higher116th or lower; S&P/ASX 200 179th or higher221st or lower; S&P/ASX 300 274th or higher326th or lower. These float-adjusted market capitalization rank buffers serve as the guidelines used by the Index Committee to arrive at any potential constituent changes to the indices. However, the Index Committee has complete discretion to bypass these rules when circumstances warrant."
So basically if a current constituent is ranked under 220th position its in the firing line for "Removal" from the ASX200 Index and if a company has managed to get to above the 180th position it is likely to be "Added" to the ASX200 index. Based on MC, but it doesn't appear to state if there is a cut-off date that the ranking applies to, or if its a weighted time period eg 20 business days prior to announcement date.
Ooops..... found it...
"Rebalancing of the S&P/ASX Australian index series occurs on a regular basis. Shares and Investable Weight Factors (IWFs) updates are also applied regularly. The reference date used for the trading data is the second to last Friday of the month prior to the rebalancing." My only question is does that (in my bold) mean it is a time period of eg the second Friday in Feb (10th today) to the last Friday in Feb (24th) I assume inclusive? And likely the closing MC on each of those 11 trading days, averaged?

page 12
"Rebalancing announcements are made on the first Friday of March, June, September, and December; therefore, a two-week notice period is provided before the rebalancing takes effect at each review. Eligible stocks are considered for index inclusion based on their rank relative to the stated quota of securities for each index within the S&P/ASX hierarchy. For example, a stock that is currently in the S&P/ASX 300 and is ranked at 175, based on float-adjusted market capitalization, within the universe of eligible securities may be considered for inclusion into the S&P/ASX 200, provided that liquidity hurdles are met. Stocks that fail the relative liquidity criteria are typically removed from the float-adjusted market capitalization rankings. At the March and September rebalancings, current constituents and stocks that pass the S&P/ASX 300 relative liquidity requirement remain in the rankings as the size hierarchy is reviewed simultaneously."

So I'm more inclined to think ARU will make it into the ASX200 index in the June rebalancing as I don't think its quite at the "179th or higher position" I think that might need a MC of around $1.45bil+ (over 0.69 SP). Bottle of Aussie Prosecco remains in the fridge for another 3 months til brunch Friday 2nd June
Stuff it.... I'll drink that one this weekend and buy a freshie for June 2nd Havagoodweekend fellow HCs.