Cash held overseas.

There’s nothing rule-breaking about leaving it out — some tax experts say it makes perfect sense — but the move could make it more difficult to gauge whether one of the federal tax changes enacted last year is stoking corporate investment in the U.S., as the Trump administration said it would.

Cupertino, Calif.-based Apple (AAPL), which at one time had $252 billion stockpiled abroad, said it plans to repatriate money, but hasn’t reported foreign cash holdings since September. Microsoft (MSFT) stopped at the end of last year. Google (GOOGL), Oracle (ORCL) and Netflix (NFLX) discontinued the disclosure this year.

The tax regime signed into law in December by President Donald Trump requires American-based companies to pay tax on money they’ve stashed outside the U.S. The new rules set a one-time rate of 15.5% on cash and 8% on non-cash or illiquid assets. Payments can be made over eight years. Previously, companies had to pay 35%, but only if they brought the money back to the U.S.

“The primary reason for the disclosure in the first place was that cash located in a foreign subsidiary was not the same as cash already in the U.S.,” said J. Richard Harvey, a professor at the Villanova University law school and graduate tax program in Pennsylvania. “It makes sense that U.S. multinational corporations would stop disclosing the amount of cash held overseas.”

But the lack of disclosure makes it more difficult to calculate whether the new tax is ending what the Treasury Department called a “perverse incentive to keep foreign profits offshore.”

Apple and Redwood City, California-based Oracle declined to comment. Google, Los Gatos, California-based Netflix and Microsoft, based in Redmond, Washington, didn’t respond to requests for comment.

Mountain View, California-based Google, for example, said in its latest quarterly statement that for March 31, 2018, it recorded a “tax liability for the one-time transition tax on accumulated foreign subsidiary earnings of $10.2 billion.” Google last reported offshore cash holdings of $62.8 billion.

Facebook (FB), which continues to disclose its overseas cash holdings, reported a record $20.1 billion last quarter. That’s $4 billion more than what it held at the end of last year.

Ending the disclosure seems to be more exception than rule. Tech giants like Qualcomm and Cisco Systems have continued to put out a number. So have Coca-Cola and rival PepsiCo, as have companies such as Caterpillar and General Electric. Of those companies, Coca-Cola, Caterpillar and GE have reduced their offshore holdings.

“Repatriations will be, in the grand scheme of things, relatively modest and opportunistic,” said Robert Willens, a tax and accounting adviser in New York. “I’m not sure that companies, certainly at this stage of the business cycle, are going to aggressively expand their plant and equipment balances in anticipation of even greater demand for their products.”