Certainly am, and yes the corrected price can go negative. Same with historic commodities data. Apparently that's OK for backtesting purposes - moving average, Donchian, Bollinger band systems still work OK.
Am looking forward to my since-purchase THL adjusted share price going negative soon, and AIR in a couple of years.
I guess that is true of the break-up value of the company - it is worth 5c less.
But I look at it this way.
Say the company's share price was $1. It paid a 5c unimputed dividend. I then pay tax on that dividend (let's say at 28%). I'm left with 3.6c. If, as you say, the correct ex price is 95c - then adding 3.6c gives 98.6c.
In theory, the market will price shares so that the shareholders are no better or worse off after a share goes ex.
If most shareholders pay around 30% tax, they will price that share such that when it goes ex, it is worth 3.6c less. Not 5c.
Otherwise, shareholders would be selling the company before it goes ex, to avoid the above 1.4% capital loss. And maybe buying back after.
Non-accountant logic. Fire at will.
Personally, I ignore both. The discount on DRIP is trivial - say 5% of a 3% div, taken up by 20% of shareholders.
And (as I understand it) the company gets that supplementary dividend back as a tax credit.
A final off-topic thought - the NZ50 is supposed to be a benchmark, against which NZ investors measure their performance.
No investor can match the NZ50 by copying the NZ50 because:
1) NZ50 pays no tax on non-imputed dividends - investors do.
2) Trading costs - brokerage, slippage.
3) NZ50 reinvests dividends on the day they go ex - investors must wait till the dividends are paid.
All in all I reckon the true annual benchmark is at least 2% below the NZ50's performance.